1. Field of the Invention
This invention relates to an apparatus for producing a thin film of tantalum oxide, which is suitable for use as a capacitive insulating film of DRAMs (dynamic random access memories) for example.
2. Prior Art
In recent years, as a useful method for making a thin film of semiconductor or of dielectrics chemical vapor deposition (CVD) has been given attention, which consists of thermally decomposing and/or causing raw material gases to react in a vacuum chamber to form a film on a substrate. CVD is considered useful for making a thin film of tantalum oxide used as capacitive insulating film of semiconductor memories, and various methods have been tried, with a CVD apparatus comprising a vacuum chamber capable of being raised to a high temperature, to form a tantalum oxide film.
In the following, explanation is made on a conventinal apparatus for producing a thin film of tantalum oxide, referring to a schematic view given by FIG. 1.
The vacuum chamber 1 in which a substrate 3 consisting of polysilicon or tungsten silicide or such is laid is exhausted by a vacuum pump 2 to 0.5 to 10 Torr, and heated by a heater 4 to about 450.degree. C. A raw material of liquid organic tantalum compound, for example, Ta(OC.sub.2 H.sub.5).sub.5 is prepared in an ampule 5, which is kept at 120.degree. C. by a heater 6. The organic tantalum compound is carried by a inert carrier gas 8 such as He or Ar to a leading pipe 10, the carrier gas 8 being controlled by a flow controller 7 and bubbling in the ampule 5, and the leading pipe 10 being heated to about 150.degree. C. by a heater 9. The carrier gas 8 containing tantalum compound is mixed with an oxygen-containing gas 12 in the leading pipe 10 to form a mixed gas, which is introduced into the chamber 1. The amount of flowing of the oxygen-containing gas 12 is controlled by a flow controller 11. The mixed gas introduced into the chamber 1 is thermally decomposed and reacts, and a thin film of tantalum oxide is formed on the substrate 3.
However, the CVD apparatus as described above had the shortcomings that, the organic tantalum compound, with a change of temperature of surrounding atmosphere or of heating temperature by the heater 6, has its temperature and flowing amount changed, resulting in difficulty of forming a film of uniform quality.
Also, the film-forming speed of the apparatus was slow, since the content of tantalum compound and oxygen in the mixed gas introduced into the chamber 1 is small due to necessary large amount of the carrier gas for bubbling.